Armature Symmetrizing Problems
I feel a little silly answering my own question so quickly, but this was easy to miss so it is best to make sure it is documented.

The shin didn't symmetrize because the name was ever so slightly off. I had "shin.L**.**" instead of "shin.L". That extra dot on the end was enough to confuse Blender into not working properly.

Keep a sharp eye on your bone's names.